Field of the Invention
The present invention relates to a comparator circuit, an imaging apparatus using the same, and a method of controlling the comparator circuit.
Description of the Related Art
Generally, a configuration of an analog-digital (A/D) converter includes a comparator. The A/D converter is used, for instance, for an imaging apparatus. For the imaging apparatus, there is a technique of connecting the A/D converter to each column of pixels arranged in rows and columns, and converting an analog signal output from each of the pixels into digital data by the A/D converter. Some A/D converters include a differential-input and single-end-output type comparator. There is a variation of offset voltage between input terminals of each of the comparators, among each of the columns. As a method of reducing this variation, a technique is known which cancels an offset voltage as described in Japanese Patent Application Laid-Open No. 2010-16656.
However, in an offset voltage canceling method described in Japanese Patent Application Laid-Open No. 2010-16656, an input voltage range of the comparator is limited depending on a voltage between a gate and a source of a transistor which constitutes a current mirror circuit of a comparator. For this reason, depending on the performance of the transistor, the input voltage range of the comparator may not be sufficiently wide with respect to the input voltage range of the pixel signal.